Close between 6
♠ and 6
♦. I think I'd go with 6
♦.
While in lower-level slam exploration, I endorse bidding cheaper cues rather than strictly 1st round v 2nd round, that is based on the idea of conserving space, where we will have room for several rounds of cue bids and maybe even keycard at some point. Here, 6
♦ is to be preferred over 6
♣ because you should NOT be bidding 2nd round controls as your first cuebid in a 6-level probe for 7.
To suggest that partner needs the
♣A to cue 6
♦ is wrong...just as it is wrong to think that he will cue a diamond control lacking the A.... the partnership lacks the bidding space to distinguish 1st from 2nd.
While the actual hand makes it clear that a 6
♦ cue from partner would be 2nd round control, basing the meaning of bids on the cards you actually hold is weak. Consider Axxxx A xx AKxxx opposite KQJxxx x AKxx xx.
How should these hands bid? Wouldn't we have the auction the 6
♣ cue bidders are suggesting? So when partner is looking at his hand over 6
♣ do we really want him cuing 6
♦ on KQJxxx x KQJxx x?....
This is just a quick example of why you need to be cuing 1st round controls, so please don't quibble with the exact hands.... .if you disagree with me (Ken?), please argue from principle rather than poking a hole in a specific example
6
♦, otoh, is pretty clear: 1st round control, no first round control in clubs, but interest in grand slam if opener controls the rounded suits. That looks like a good working description.
However, it is possible to construct hands on which he accepts and we have virtually no play... so it is entirely possible that the pragmatic 6
♠ will be the winning call.....not to mention that the odds that they can cash a heart must approach 95% on this auction, so looking for grand may be chasing moonbeams.
'one of the great markers of the advance of human kindness is the howls you will hear from the Men of God' Johann Hari